Last week, when the Colts traded for then-Browns' RB Trent Richardson, social media was abuzz with debate on the winners and losers of the trade. One of the most interesting arguments centered around just how good Richardson was with many people noting his lifetime yards-per-carry (ypc) average of just 3.5ypc. The most common reply to these concerns focused on Trent Richardson's position as the only credible offensive weapon on the Browns, and how the lack of a respectable passing game allowed defenses to shut him down.

This answer intrigued me. It's one of those answers that is readily accepted because it seems perfectly logical. But at the same time, I wanted to know: was it true?

So, I set out on a quest to find out just that. What follows is not trade analysis. I am not going to tell you who wins or loses a trade less than a week after it was made. What we'll be looking at is what effect, if any, a strong passing game has on the running game and vice-versa.

Before I inundate you with tables and numbers, let me first explain how I approached the problem. First, I believe that since the illegal contact emphasis, the NFL has slowly moved more and more towards being a passing-dominated league. Recent rules governing player safety have done nothing to slow or alter this process. With that in mind, it is my opinion that the "latest era" of NFL offenses began in 2005.

So for this study, I gathered as much data as possible from 2005 to 2012.

In Part 1, we will focus entirely on conventional (non-advanced) stats. I chose two stats for this portion of the program: passing yards-per-attempt and rushing yards-per-attempt.

"Greg, why did you choose yards-per-attempt instead of yards?"

For a few reasons. First, the entire discussion about Trent Richardson revolved around his career YPC, so keeping this study in the same context makes for easier comparisons. Second, pure yardage is often a function of attempts. A bad running team can still rack up the yardage because they run the ball a lot. Third, if the theory is that passing leads to a better running game, then your per-play numbers should be more explosive.

So I took the 10-best and 10-worst passing and rushing teams for those 8 years (2005-2008). I then found each team's corresponding complementary ranking (for example: in 2005 Indianapolis has the 2nd-ranked passing offense in the league by y/a, their corresponding complementary ranking is the 24th-ranked rushing attack).

"Greg, if this is your explanation… it's going to be a long day."

I know. We're almost done. Once I had each year divided into 4 groups, I found the average yards-per-attempt for each group's complementary ranking and then compared it against the league average for that year. In other words, after I had the top-10 passing leagues, I found the average rushing ypa for those top-10 passing offenses, and compared THAT average against the league average. So did the top-10 passing offenses have better-than-average rushing attacks? Below-average?

I did that for all 8 years. It was fun. Below, the stats, as neatly-presented as possible. I apologize for all of the tables. I'm very sorry. Whatever pain your eyes feel, my soul feels double. Enjoy.

Tables for 2005:

Thoughts, notes and observations for 2005:

Nothing too notable here. The top passing attacks had a slightly above average rushing YPA and the bottom passing attacks had a slightly below average rushing YPA.

Meanwhile… both the top and bottom rushing attacks had slightly above average passing attacks? Being stuck in the middle stinks.

The best passing attack in the league yielded the 12th-best rushing attack. The worst passing attack in the league yielded the 7th-best rushing attack.

The best rushing attack in the league yielded the 21st-best passing attack. But Michael Vick was the QB…. The worst rushing attack in the league yielded the 12th-best passing attack.

Tables for 2006:

Thoughts on 2006:

Up is down and down is up! Here in opposite land: The best passing AND rushing attacks yielded slightly below average rushing and passing attacks

While the worst passing and rushing attacks yielded slightly above average rushing and passing attacks.

Seriously, you can't explain that!

The best passing attack in the league had the 15th-best rushing attack, while the worst passing attack in the league had the 24th-best passing attack. Here's a reminder: Jon Gruden ruined Tampa Bay.

The best rushing attack in the league had the 23rd-best passing attack. But again, Michael Vick. The worst rushing attack in the league had the 10th-best passing attack. Kurt Warner was good.

Tables for 2007:

Thoughts on 2007:

Tom Brady loves Randy Moss.

Adrian Peterson is really good. This is his rookie year. His QB was Tavaris Jackson. Yep.

2007 should also be renamed: the year when every horrible player inexplicably had a career year. It's so weird. One good year in a sea of poop.

The most notable thing here? The best rushing attacks gave a noticable uptick to passing attacks, moving those passing attacks .3ypa above average.

The best passing offense in the league had the 12th-best rushing offense. While the worst passing offense in the league had the 14th-best passing offense.

The best rushing offense in the league had Tavaris Jackson. The worst rushing offense in the league had the 21st-ranked passing offense.

Tables for 2008:

Thoughts on 2008:

Not too much out of the ordinary here. Most years we see slight movement (.1) above or below average. This year, the biggest difference is seen with the worst rushing offenses, which produced passing offenses .2ypa below average.

The best passing offense had the 19th-ranked rushing offense, while the worst passing offense had the 26th-ranked rushing offense.

The best rushing offense had the 18th-ranked passing offense, while the worst rushing offense had the 12th-best passing offense.

2008 was the year Peyton Manning played on one leg. People forget that the offensive line was also in tatters (Jeff Saturday missed time). The running game was useless. But Manning still provided the Colts with a legitimate passing attack. While compiling these stats, the biggest take away, with regards to Peyton Manning, was just how consistent he was. Yes, he's one of the best, but what makes him THE BEST, in my mind, is that he was one of the best, year-in and year-out. So hard to do.

Tables for 2009:

Thoughts on 2009:

So here's the first realy interesting thing I noticed: this was the year the Vikings acquired Brett Favre. Favre gave the Vikings an elite passing offense (4th). This was also the year that Adrian Peterson and the Vikings had their worst rushing offense. It's not a matter of losing carries, this was a YPA study. It's really weird. I guess I would have to look closer at the Vikings, maybe there were some injuries there.

The best passing and rushing offenses produced slightly below average rushing and passing offenses. The worst passing and rushing offenses produced average rushing and passing offenses.

The best passing offense had the worst rushing offense, while the worst passing offense had the 15th-ranked rushing offense.

The best rushing offense produced the 21st-ranked passing offense. This is Chris Johnson and Kerry Collins. Another rookie RB producing elite numbers despite bad QB play

Tables for 2010:

Thoughts on 2010:

Some logical results! Slightly above average corresponding production from the best offenses, slightly worse corresponding production from the worst offenses.

We see the Colts continue to struggle running the ball. This is the first year we've seen real slippage from the passing game (at least via conventional stats). Also Manning's last year (on the field) in Indianapolis

The best passing offense produced the 22nd-ranked rushing offense. The worst passing offense produced the 12th-ranked rushing attack.

The best rushing offense produced the 6th-ranked passing offense. The worst rushing offense produced the 20th-best passing offense.

Tables for 2011:

Thoughts on 2011:

LOOK AT THE PACKERS YPA!!! The league average in passing ypa takes a jump this year, as well.

3 of 4 cases keep with the trend: within .1 of league average. The only "outlier"? The top-10 rushing attacks pushed their corresponding passing games .2ypa above average.

Philip Rivers, while a jerkface, deserves some love: San Diego consistently had one of the best passing attacks while he was the QB. But while Rivers, Gates, and Tomlinson got all of the headlines, maybe Vincent Jackson was the MVP of that team? The team's ypa remained strong through injuries to Gates and the decline and eventual departure of Tomlinson, but it was Jackson's exit at the end of 2011 that sent the Chargers' offense flying off the map.

The best passing offense in the league produced the 26th-best rushing attack, while the worst passing offense produced the 23rd-best rushing offense.

The best rushing attack in the league produced the 8th-best passing offense in the league while the worst rushing attack produced the 3rd-best passing offense in the league.

Tables for 2012:

Thoughts on 2012:

Again, that weird thing: both the best and worst passing offenses produced above average rushing attacks.

Outside of that, the better rushing offenses produced better passing attacks and the worst rushing offenses produced below average passing attacks.

One thing I really look forward to seeing: the top-4 passing offenses were all led by mobile quarterbacks. All 4 of those offenses had dominant running attacks. This is the wave of the future. This is why I've been begging the Colts to let Andrew Luck be Andrew Luck.

The best passing offense had the 2nd-best rushing offense. The worst passing offense had the worst rushing offense. But it's Arizona. Does that really count?

The best rusing offense had the 31st-best passing attack. Let me remind you: A RUNNING BACK SHOULD NEVER EVER EVER (EVER EVER) WIN THE NFL MVP AWARD. NEVER.

Final Thoughts/Summary Tables:

While 8 years provided an enormous amount of data, I'd still say it's a relatively small sample size. As I believe we're playing a different game now, I don't think we'd learn too much from going further into the past. Instead, I'll have to add on to the numbers in the coming years.

Just to reiterate: this is not about the Trent Richardson trade. No data here and no statistics from Sunday will tell the story of that trade.

There are a lot of variables I can't consider. Namely the play of the offensive lines. Most metrics will judge an O-line in run blocking by how well the running game performs. Well, is that the blocking or the running back? Probably a mixture of both.

While there seems to be real discernible pattern, that may change: there was definitely a trend in the past 3 seasons that saw the top passing offenses have better rushing offenses AND the best rushing offenses having better-than-average passing offenses.

In that same period, the bottom passing and rushing defenses both produced below average counterparts.

We should also note, that while the average passing YPA started to slowly climb in 2009, the average rushing YPA has also slowly climbed. Basically, offenses are just OUT OF CONTROL.

Fun with math: From 2005 to 2012, there were 80 top-10 offenses and 80 bottom-10 offenses (8 years x 10 teams = 80!). So if a Top-10 passing offense produced a top-10 rushing offense 30 times and a bottom-10 Pass offense produced a top-10 rushing offense 21 times, that means an average (11th through 22nd) passing offense produced a top-10 rushing offense 29 times. Averages: Top-10: 3.75 top rushing offenses per year, Middle-12: 3.625 top rushing offenses per year, Bottom-10: 2.625 top rushing offenses per year.

This probably should have been another table. But seriously, I can't stand another table.

As you can see, there is definitely a difference, but it's about 3/4 of a team, per year.

Overall, I think if we learned anything, it's that good offenses are good offenses and bad offenses, by-and-large, are bad offenses. There are exceptions: Peyton Manning doesn't need your running game. Neither do Tom Brady and Aaron Rodgers. And Adrian Peterson doesn't need your passing game. Neither do Chris Johnson or Jamaal Charles. I don't think having a great passing offenses makes it significantly easier on your running game, but I simply don't have enough data.

Which brings me to this: these are just conventional stats. They are fine, they help us tell the beginning of a story, but they don't allow us to tell the whole story. As the title of this piece suggests, this is not a 1-Part endeavor. I'll be adding on to this every week. Next week we're going to take a look at advanced stats, specifically Football Outsider's DVOA and ProFootballFocus' signature stats. All-in-all, I expect there will be quite a few parts to this. I also want to look at the relationship between having a dominant wide receiver and the running game. I also want to look at the effect "star" power has on the offense. We generally know who the top-5 "names" at quarterback are each year. We generally know who the media, fans, and players consider to be the top-5 running backs in the league each year. Does having one of these "star" players have an impact on the offense?

After those three (advanced stats, wide receivers, "stars"), I also want to look at whether or not having a strong running game actually affects the opposing pass rush. This has been stated a few times in the past month, and I'm not sure if it's true or not. So we'll find out in a month or so.

I want to give a special thank you to Kyle Rodriguez for building those pretty tables for me, and to Meagan Terlep and my wife (who shall remain safely anonymous) for helping me gather some of the stats.